For vehicle-to-vehicle distance control, a vehicle-mounted radar system, which projects a radar beam forward and thereby detects an object such as a vehicle traveling ahead, is used. Examples of this type of radar system include FM-CW radar that uses a radio wave such as a millimeter wave and radar that uses laser light. Using such a radar system, the distance and relative velocity with respect to the vehicle ahead and the actual position of the vehicle ahead are detected to control the vehicle-to-vehicle distance. To detect the position of the vehicle traveling ahead, it is important that the approximate center position of the vehicle be detected.
However, when the target vehicle traveling ahead is a large vehicle such as a truck, for example, a number of peaks may appear in the signal reception level when a plurality of transmitted beams are reflected from the target. In such cases, it is often difficult to determine which peak represents the center of the target.
Furthermore, when the target is a large vehicle, the beams reflected from a plurality of differently located parts of the same target may be erroneously recognized as being reflections from different targets. Further, when the large vehicle is traveling in the neighboring lane, the beam that hit a front side mirror or nearby portion of the vehicle is reflected toward the same lane as the radar-equipped vehicle, and this reflection may be erroneously recognized as being a reflection from a vehicle traveling ahead in the same lane as the radar-equipped vehicle.
Further, when beams are reflected from a plurality of differently located parts of the same target, pairing between the peak frequencies in the rising and falling portions of the reflected signal from each of these parts has to be done in order to detect the distance and relative velocity of each of the differently located parts.
Accordingly, an object of the present invention is to make provisions to be able to correctly locate the center of a target even when the target is a large vehicle. Another object of the invention is to make provisions to be able to identify whether reflections arriving at the radar are from the same target or not, even when the target is a large vehicle, or the like, that reflects beams from a plurality of portions thereof. Still another object of the invention is to make provisions so as not to erroneously recognize a vehicle traveling in the neighboring lane as being a vehicle traveling in the same lane as the radar-equipped vehicle. A further object of the invention is to accomplish efficient pairing between the peak signals of the beams reflected from a plurality of different portions of the same target.